The production of workpieces (e.g, disks) used in the magnetic disk drive industry begins with the creation of a substrate with a hard smooth surface upon which magnetic material is deposited. Fabrication of a magnetic disk typically involves lapping or honing a disk substrate, such as, aluminum, to a high degree of flatness with as smooth a finish as is possible. With some substrates, such as aluminum, intermediate layers of hardeners such as amorphous NiP coatings are applied. The substrate disks are then polished to a much higher degree of smoothness. Magnetic media is then typically sputtered onto the substrate surface, buffed to remove micro-asperities, and toughened with hard coatings and lubricants.
A disk drive operates by passing a read-write head over the surface of the disk. Because the read-write head passes over the disk in very close proximity, it is important for the disk to have a very flat, smooth, or controlled micro-roughened surface. If the surface of the disk is overly rough or uneven, the read-write head may touch the disk or "crash," causing permanent damage to the disk drive and resulting in a loss of data. As disk drives evolve with greater memory capacities, read write heads fly closer to the memory disks. Thus, defects and minute waves on the disks are becoming an even bigger problem with memory disk evolution.
Lapping, honing, and polishing workpieces or disks coated with hard material is well known in the art. These processes generally include placing the workpiece in a carrier, placing the carrier and workpiece between two platens, each having the appropriate abrasive composition or surface attached thereto, and moving the carrier (and hence the workpieces) relative to the abrasive surface.
Abrasive surfaces can be formed of various materials, as is known in the art, and which are available commercially. Typically, the lapping or honing surface is formed from a resin bonded silicon carbide grinding stone, for example, a stone manufactured by Kanebo oe Nitokken of Japan. The removal rate and variability of the stock removal across the surface of the workpiece depends on several factors, including the composition and condition of the abrasive surface.
During these processes, the micro-structures of these abrasive surfaces wear and are eventually crushed from the load on the surfaces, causing them to become less effective. Accordingly, to increase the effectiveness and life of these surfaces, it is desirable to condition the worn surfaces, for example, by removing a portion of the surface material and any excess debris that may reside on them, thus exposing a fresh abrasive surface.
Referring now to FIG. 1, one well known method for conditioning the lapping, honing, or polishing surface is to roughen the surface with one or more conditioning plates or carriers 10 which include pellets 20 having abrasive particles (not shown) attached thereto. In accordance with this well known method, pellets 20 are typically cylindrically shaped and are attached to one surface of carrier 10, by, for example, brazing or glueing the pellets to one surface of carrier 10.
Generally, an upper and a lower abrasive platen surface, are conditioned on a machine at the same time by placing conditioning carriers 10 between the upper and lower abrasive surfaces. The conditioning of the polishing surfaces proceeds by placing a number of the conditioning carriers 10 with their abrasive side down to condition the lower polishing surface and placing an equal number of conditioning carriers 10 with the abrasive side up to condition the upper polishing surface. The upper platen surface functions as a reference plane for the conditioning carriers 10 with the abrasive side toward the lower platen surface, and the lower platen surface functions as a reference plane for the conditioning carriers 10 with the abrasive side toward the upper platen surface.
This well known conditioning process has several shortcomings, particularly on softer abrasive platen materials such as honing stones and polish pads. For example, during the conditioning process, the individual pellets 20 typically exert localized pressures on the abrasive surface, thereby deforming the surface by creating multiple moving indentations therein. In addition, these indentation tracks caused by pellets 20 typically overlap; however, because of the elastic behavior of the materials being dressed, such as honing stones, polish pads, and the like, the stones and pads typically recover in the areas between the pellets (i.e., in the areas where tracks do not overlap). Thus, the overlapping wear of the pellets form "waves" on the surface of the honing or polishing materials which, in turn, create a micro-waviness on the workpiece surfaces. Moreover, because of the geometric configuration of the conditioning carrier 10 of FIG. 1, (i.e., pellets covering a substantial portion of the carrier) the wear caused by the pellets on the outside diameter of the carrier is not uniform with the wear caused by the inside pellets. In other words, as the carrier 10 rotates and orbits about the abrasive loaded platens, the inside pellets cover a lesser area of the stone or polish pad.
Accordingly, new methods and apparatus for conditioning the surface of a polishing material are therefore needed that overcome the limitations of the prior art.